cis-acting regulatory elements in the GAP-43 mRNA 3 '-untranslated region can function in trans to suppress endogenous GAP-43 gene expression

The expression of the GAP-43 gene is controlled partly by changes in the st ability of its mRNA, a process that is mediated by the interaction of speci fic sequences in the 3'-untranslated region (3'UTR) with neuronal-specific RNA-binding proteins. Limiting amounts of these trans-acting factors are av ailable in the cell, thus we proposed that overexpression of the GAP-43 3'U TR could affect the levels of the endogenous mRNA via competitive binding t o specific RNA-binding proteins. In this study, we show that chronic expres sion of GAP-43 3'UTR sequences in PC12 cells causes the depletion of the en dogenous mRNA and consequent reduction of GAP-43 protein levels. The levels of the mRNAs for c-fos, the amyloid precursor protein (APP) and the microt ubule associated protein tau, all three containing similar 3'UTR sequences, were not affected by the treatment. These results thus suggest that the ef fect of excess GAP-43 3'UTR is specific for its corresponding mRNA. We also used an HSV (herpes simplex virus)-l vector and a mammalian expression vec tor with an inducible promoter to acutely express a 10 to 50 fold excess of 3'UTR sequences. Under these conditions, we found that transient expressio n of the GAP-43 3'UTR was effective in inhibiting both GAP-43 gene expressi on and neurite outgrowth in nerve growth factor (NGF)-treated PC12 cells an d in primary neuronal cultures. These results underscore the role of 3'UTR sequences in the control of GAP-43 gene expression and suggest that overexp ression of specific 3'UTR sequences could be used as a potential tool for p robing the function of other post-transcriptionally-regulated proteins duri ng neuronal differentiation, (C) 1999 Elsevier Science B.V, All rights rese rved.